Acid-treated clay materials (Southwestern Tunisia) for removing sodium leuco-vat dye : Characterization, adsorption study and activation mechanism

Clay deposits of El Haria formation (Jebel Stah of the Gafsa basin, Southwestern Tunisia) was treated with sulfuric acid to improve its surface properties and dye adsorption ability. Acid treatment was carried out at 60 °C, by varying time of treatment from 0 to 6 h. The influence of activation was investigated using X-ray Diffraction (XRD), chemical analysis, Fourier Transform Infra-Red (FTIR) spectroscopy, specific surface area (SSA), and cation exchange capacity (CEC). The raw clay contained a major phase of smectite and kaolinite, in addition to quartz, feldspars, calcite and dolomite as impurities. Acid treatment led to the dissolution of cations, such as Al 3+, Mg 2+ and Fe 3+ from the octahedral sheets and thus increased surface acidity, specific surface area and porosity of the material. The surface area could be greatly changed as a function of time of treatment, and it increased from 450 to 590 m 2 g −1. The adsorption ability of acid activated clay was investigated using sodium leuco-vat dye as a typical pollutant. The effects of contact time, pH and temperature were studied in batch mode. The adsorption equilibrium was analyzed by Freundlich and Langmuir models. The results revealed that Langmuir isotherm provided a better fit to the experimental data. The modified clay showed a higher removal efficiency for dye (88%) than raw material, with a maximum adsorption capacity of 15.45 mg L −1. Thermodynamic parameters suggested endothermic and physical nature.